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Guest Ron Freimuth

Engine modelling is incorrect. How would one change it?

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Caveat: programming my VCR and doing some stuff with macros is about the limit of my experience.The aspect that is wrong is that when the prop lever is pulled back on one of the constant speed planes, the fuel flow shoots up. This shouldn't happen, as the pistons are turning slower and less fuel/air is coming through the induction system. Over on a simflight.com FAQ it says that this is in fact correct performance, but this contradicts real life and logical evidence.Where is the data that governs engine performance found? Is it feasible to manipulate it?Thanks in advance.

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I am not an expert but as far as I know fuel flow primarily depends on manifold setting (power) alone. It is true that with lower rpm props are turning slower but they also have a lot more resistance to overcome due to higher blade angle. So in the "first-order" of approximation fuel flow should in fact remain constant.Michael J.

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<<<>>>Not according to this in-flight data from a real engine logging parameters as it was flown.http://www.avweb.com/articles/pelperch/pelp0008.html(Scroll down and have a look at the charts. They are annotated, and it clearly shows that when this pilot pulled the prop control back without touching the throttle, the fuel flow dropped.)Also, manifold pressure is simply a combination of how open the throttle plate is and how much the pistons are sucking air.<<<>>The prop control sets a desired RPM, not a desired blade angle. The blade angle will initially increase, loading the engine and slowing it down. Then, the governor will change the angle to maintain the desired setting. <<<>>Once again, it isn't this way in real-flight data. And in FS2002 it actually goes UP.I am certainly no expert either, but I'm very close to sure that the way it is in FS2002 is wrong.

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<<< It is primarily about mixture leaning techniques. Nothing in this article contradicts what I said - fuel flow is proportional to the work performed by the prop.>>>Yup, it is primarily about mixture leaning (fascinating series of articles aren't they, by the way?), but at this point in logging the data the mixture control hasn't been touched. All that has been touched is the prop control: from 2700 RPM to 2500 RPM. The fuel flow clearly goes down, yet in FS2002 it goes up by a pretty huge amount. That's the behaviour that's puzzling me.

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Vmca...That's a good article. I've bookmarked it for a later reading.I haven't noticed your issue as much as I have that when we change the mixture on the engines,we don't see any change in fuel flow, CHT or EGT.So, when I'm decending from or climbing to an alitude, I just pretend that I'm changing fuel flow...I go through the motions.If it bothered me bad enough, I guess I'd learn how to design gauges.http://www.cableone.net/joesumralliii/hook.gif

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The article touches upon the favorite discussion topic - how to lean - on the rich or lean side of the curve. The last issue of FLYING has a big article on the subject. Needless to say it is a highly debated, controversial subject, even Lycoming and Continental engineers are not in full agreement.Michael J.

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<<<>>>And how. Even more so than religion and politics.

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>I am not an expert but as far as I know fuel flow primarily >depends on manifold setting (power) alone. It is true that >with lower rpm props are turning slower but they also have a >lot more resistance to overcome due to higher blade angle. >So in the "first-order" of approximation fuel flow should in >fact remain constant. >>Michael J.I take it back .. Michael J.

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>The aspect that is wrong is that when the prop lever is >pulled back on one of the constant speed planes, the fuel >flow shoots up. This shouldn't happen, as the pistons are >turning slower and less fuel/air is coming through the >induction system. Over on a simflight.com FAQ it says that >this is in fact correct performance, but this contradicts >real life and logical evidence. >>Where is the data that governs engine performance found? Is >it feasible to manipulate it? MSFS people must not know much about engines. TBL 508 is wrong in many of their AIR files. Torque increases a lot around 2100 RPM. This is incorrect.Ron

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<<<>>>As chance would have it, I d/l'd the superb 421C Golden Eagle and, lo and behold the engines behave as they should.Obviously, it ~is~ possible for it to be modelled correctly in FS2002. It just isn't in the default planes.

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So you like Flight1's Cessna 421C ?Tell me about its flight director (not sure it has one). But in case it has one is it working correctly ? For some reason this piece of instrument is giving many developers trouble yet FS2002's default airplanes have it working just fine.Michael J.

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Hi. You are right. All, or most, MSFS engine/flight dynamic models are not correct. If you want something that you can use, you have to look/beg for the Ron and Steve

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<<>>It doesn't.One other thing it doesn't seem to have is an ADF or an RMI (unless I'm mistaken). I'd really like to add one because we still have plenty of them here in Australia.However, IMHO, it's a great plane.

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>It doesn't. Interesting. Nowadays planes that cost 1/2 that much are equipped with one.I read about instrument refreshment rate that can be set by user. So how smooth are the instruments ? What's the overall performance - how does it compare to the default airplanes ? Thanks.Michael J.

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<<>>I have yet to fully explore the package, but I think you might be referring to the GPS. I definitely know you can set the refresh rate on that.<<>>Pretty smooth so far, although my frame rates seem to have taken a bit of a hit. I'm going to look into it and see what tweaking I should do.<<>It's got that "right" feeling, IMHO. I'm a big fan of piston twins, and this feels better to me than the default Baron, more stable and logical in the way it flies. The caveat is I'm no expert on either planes. The closest thing I've flown (and low hours at that) is a Piper Chieftain.I'm going to play around doing some asymmetric work and see how it feels.All in all though, I'm really impressed. I am going to ask here if there's any way of putting an ADF into the panel, though.

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>Hi. > You are right. All, or most, MSFS engine/flight dynamic >models are not correct. >If you want something that you can use, you have to look/beg >for the Ron and Steve

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Hi. Thank you, Ron. I was not sure about the distribution, I recall reading something about it. Thank you for all your effort. I have an .air file that I modified, empirically, since I am not sure what some of the elements do, and how they interact with each other, and after spending many hours of trial and error, the .cfg got munched up by FSEdit? Now I have to start a new .cfg. What fun! I hope you reconsider and give us amateurs a break. Thanks again for all you

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>Pretty smooth so far, although my frame rates seem to have >taken a bit of a hitHow about the 2D panel alone ?. I understand that VC could cause fps hit but 2D panel should be much faster.Michael J.

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Michael,On my system, the VC panels outdo the 2D's usually 5 to 10 fps in nearly all cases. Default & 3rd party.With the Archer, Cheyenne, Falcon 50, & C421, I'm liking the VC's all the better!L.Adamson

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>Hi. > Thank you, Ron. I was not sure about the distribution, I >recall reading something about it. Thank you for all your >effort. I have an .air file that I modified, empirically, >since I am not sure what some of the elements do, and how >they interact with each other, and after spending many hours >of trial and error, the .cfg got munched up by FSEdit? Now I >have to start a new .cfg. What fun! Using FSEDIT is dangerous unless you only modify certain things. Such as moments of inertia, weight, payload, and a few others. If one changes the Wing Sweep, or any of many other things FSEDIT (or FS2K2) is likely to add a bunch of new sections to the AIR file. With it's idea of what many parameters should be. Unfortunately, such AIR files usually have bad flight dynamics. Save a BU of the AIR file and see that the regular file stays the same length as the BU! I generally edit aircraft.cfg. But, have to be careful or the same thing can happen. FS2K2 doesn't change things already set in aircraft.cfg but if one doesn't have everything already set it can end up messing up the AIR file and/or Aircraft.cfg Many AC parameters, including those relating to the tail surfaces, have NO EFFECT. Unless one lets FSEDIT/FS2K2 make the additions to the AIR file. Others are very important, such as Wing Area. It's only becaues I have some understanding of what is going on that I've avoided such problems after the first month or so of importing FS2K AC into FS2K2. If I do find the added records in an AIR file I remove them with Aired. Incidently, I've figured out what a lot of them do, but have no reason to not use the old records for FS2K2 AIR files.> I hope you reconsider >and give us amateurs a break. Thanks again for all you

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Hi. Thanks for your feedback. I never invoked FSEdit. It would seem the MSFS will do that on it

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>Hi. > Thanks for your feedback. I never invoked FSEdit. It would >seem the MSFS will do that on it

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